The present invention relates to addressing apparatus for electronic displays and, in particular, to rear electrode structures for encapsulated electrophoretic displays.
Traditionally, electronic displays such as liquid crystal displays have been made by sandwiching an optoelectrically active material between two pieces of glass. In many cases each piece of glass has an etched, clear electrode structure formed using indium tin oxide. A first electrode structure controls all the segments of the display that may be addressed, that is, changed from one visual state to another. A second electrode, sometimes called a counter electrode, addresses all display segments as one large electrode, and is generally designed not to overlap any of the rear electrode wire connections that are not desired in the final image. Alternatively, the second electrode is also patterned to control specific segments of the displays. In these displays, unaddressed areas of the display have a defined appearance.
Electrophoretic display media, generally characterized by the movement of particles through an applied electric field, are highly reflective, can be made bistable, and consume very little power. Encapsulated electrophoretic displays also enable the display to be printed. These properties allow encapsulated electrophoretic display media to be used in many applications for which traditional electronic displays are not suitable, such as flexible displays. The electro-optical properties of encapsulated displays allow, and in some cases require, novel schemes or configurations to be used to address the displays.
An object of the invention is to provide a highly-flexible, reflective display which can be manufactured easily, consumes little (or no in the case of bistable displays) power, and can, therefore, be incorporated into a variety of applications. The invention features a printable display comprising an encapsulated electrophoretic display medium. The resulting display is flexible. Since the display media can be printed, the display itself can be made inexpensively.
An encapsulated electrophoretic display can be constructed so that the optical state of the display is stable for some length of time. When the display has two states which are stable in this manner, the display is said to be bistable. If more than two states of the display are stable, then the display can be said to be multistable. For the purpose of this invention, the term bistable will be used to indicate a display in which any optical state remains fixed once the addressing voltage is removed. The definition of a bistable state depends on the application for the display. A slowly-decaying optical state can be effectively bistable if the optical state is substantially unchanged over the required viewing time. For example, in a display which is updated every few minutes, a display image which is stable for hours or days is effectively bistable for that application. In this invention, the term bistable also indicates a display with an optical state sufficiently long-lived as to be effectively bistable for the application in mind. Alternatively, it is possible to construct encapsulated electrophoretic displays in which the image decays quickly once the addressing voltage to the display is removed (i.e., the display is not bistable or multistable). As will be described, in some applications it is advantageous to use an encapsulated electrophoretic display which is not bistable. Whether or not an encapsulated electrophoretic display is bistable, and its degree of bistability, can be controlled through appropriate chemical modification of the electrophoretic particles, the suspending fluid, the capsule, and binder materials.
An encapsulated electrophoretic display may take many forms. The display may comprise capsules dispersed in a binder. The capsules may be of any size or shape. The capsules may, for example, be spherical and may have diameters in the millimeter range or the micron range, but is preferably from ten to a few hundred microns. The capsules may be formed by an encapsulation technique, as described below. Particles may be encapsulated in the capsules. The particles may be two or more different types of particles. The particles may be colored, luminescent, light-absorbing or transparent, for example. The particles may include neat pigments, dyed (laked) pigments or pigment/polymer composites, for example. The display may further comprise a suspending fluid in which the particles are dispersed.
The successful construction of an encapsulated electrophoretic display requires the proper interaction of several different types of materials and processes, such as a polymeric binder and, optionally, a capsule membrane. These materials must be chemically compatible with the electrophoretic particles and fluid, as well as with each other. The capsule materials may engage in useful surface interactions with the electrophoretic particles, or may act as a chemical or physical boundary between the fluid and the binder.
In some cases, the encapsulation step of the process is not necessary, and the electrophoretic fluid may be directly dispersed or emulsified into the binder (or a precursor to the binder materials) and an effective xe2x80x9cpolymer-dispersed electrophoretic displayxe2x80x9d constructed. In such displays, voids created in the binder may be referred to as capsules or microcapsules even though no capsule membrane is present. The binder dispersed electrophoretic display may be of the emulsion or phase separation type.
Throughout the specification, reference will be made to printing or printed. As used throughout the specification, printing is intended to include all forms of printing and coating, including: premetered coatings such as patch die coating, slot or extrusion coating, slide or cascade coating, and curtain coating; roll coating such as knife over roll coating, forward and reverse roll coating; gravure coating; dip coating; spray coating; meniscus coating; spin coating; brush coating; air knife coating; silk screen printing processes; electrostatic printing processes; thermal printing processes; and other similar techniques. A xe2x80x9cprinted elementxe2x80x9d refers to an element formed using any one of the above techniques.
This invention provides novel methods and apparatus for controlling and addressing particle-based displays. Additionally, the invention discloses applications of these methods and materials on flexible substrates, which are useful in large-area, low cost, or high-durability applications.
In one aspect, the present invention relates to an encapsulated electrophoretic display. The display includes a substrate and at least one capsule containing a highly-resistive fluid and a plurality of particles. The display also includes at least two electrodes disposed adjacent the capsule, a potential difference between the electrodes causing some of the particles to migrate toward at least one of the two electrodes. This causes the capsule to change optical properties.
In another aspect, the present invention relates to a colored electrophoretic display. The electrophoretic display includes a substrate and at least one capsule containing a highly-resistive fluid and a plurality of particles. The display also includes colored electrodes. Potential differences are applied to the electrodes in order to control the particles and present a colored display to a viewer.
In yet another aspect, the present invention relates to an electrostatically addressable display comprising a substrate, an encapsulated electrophoretic display adjacent the substrate, and an optional dielectric sheet adjacent the electrophoretic display. Application of an electrostatic charge to the dielectric sheet or display material modulates the appearance of the electrophoretic display.
In still another aspect, the present invention relates to an electrostatically addressable encapsulated display comprising a film and a pair of electrodes. The film includes at least one capsule containing an electrophoretic suspension. The pair of electrodes is attached to either side of the film. Application of an electrostatic charge to the film modulates the optical properties.
In still another aspect, the present invention relates to an electrophoretic display that comprises a conductive substrate, and at least one capsule printed on such substrate. Application of an electrostatic charge to the capsule modulates the optical properties of the display.
In still another aspect the present invention relates to a method for matrix addressing an encapsulated display. The method includes the step of providing three or more electrodes for each display cell and applying a sequence of potentials to the electrodes to control movement of particles within each cell.
In yet another aspect, the present invention relates to a matrix addressed electrophoretic display. The display includes a capsule containing charged particles and three or more electrodes disposed adjacent the capsule. A sequence of voltage potentials is applied to the three or more electrodes causing the charged particles to migrate within the capsule responsive to the sequence of voltage potentials.
In still another aspect, the present invention relates to a rear electrode structure for electrically addressable displays. The structure includes a substrate, a first electrode disposed on a first side of the substrate, and a conductor disposed on a second side of the substrate. The substrate defines at least one conductive via in electrical communication with both the first electrode and the conductor.